If/when ETH goes POS, every miner and their pets will move on other GPU minable alt-coins, and due to their low market capitalization (ie: the ETC, the best/biggest candidate to be mined, has only 6% market cap of the ETH), the instant injection of a huge amount of hashing rate, will pump the difficulty to the sky and in a couple of days the profit will collapse to the point that it will not be profitable anymore, because the price will not follow, since none of the other coins have the fame and solidity of the ETH or the BTC's, instead it will happen the opposite: you need to dump faster trying to earn something before the collapse.
The above will apply to every other currency out there, and less market capitalization the coin has, faster the profit will crash.
In theory the only crypto-currency that could assorbe a such huge mining power injected in a single day is the ETH itself and the BTC ...every other isn't big enough to sustain it, neither if you spread the hash-rate across them all.
The above doesn't mean that everything is lost, there could be other opportunities to use the power we have.. but forget to just jump on another currency (no matter what it is) and continue to mine like nothing has happened.
